This invention relates to fluoropolymer reinforced with fibrous liquid-crystal polymer.
The non-melt processible fluoropolymer polytetrafluoroethylene (PTFE) and melt processible fluoropolymers such as tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymers (PFA), tetrafluoroethylene-hexafluoropropylene copolymers (FEP), and tetrafluoroethylene-ethylene copolymers (ETFE) have excellent properties such as heat resistance, chemical resistance and non-stick properties. However, in spite of the excellent characteristics of these fluoropolymers, the physical properties of the fibers obtained therefrom are not always entirely satisfactory. In the melt spinning step in particular, the very high melt viscosity of fluoropolymers compared with other engineering plastics creates a number of problems, including greater difficulty in spinneret design and the need for effective measures against filament breakage during take-off. Also, in subsequent steps such as drawing of the melt-spun filament, the lower modulus of fluoropolymers compared to other engineering plastics, greatly hinders stable operation. Moreover, fluoropolymers have a large linear expansion coefficient, and so high-temperature shrinkage of the fluoropolymer filaments is great.
Modification of a fluoropolymer/liquid-crystal polymer composite so as to enhance the fluoropolymer matrix strength has been proposed. During extrusion, the liquid-crystal polymer is oriented in a fibrous form within the fluoropolymer matrix, thereby enhancing the matrix strength. This is discussed in Journal of Macromolecular Science, Chemical Physics 1995, C35, p. 183; and in JP-A 2-32147. The resulting extrudate exhibits an increase in strength because of the presence of oriented fibrous liquid-crystal polymer, but not all the liquid-crystal polymer is fiberized by the extrusion process and the dispersion of the liquid-crystal polymer within the extrudate is not uniform. Compared with resins reinforced using conventional reinforcements such as glass fibers and carbon fibers, advantages offered by this approach include a decrease in melt viscosity and the simplification of all the processing steps that is made possible by the use of liquid-crystal polymers.
However, the mechanical strength of fluoropolymer/liquid-crystal polymer composite fibers obtained by melt spinning is strongly influenced by the interfacial bonding forces between the fluoropolymer matrix and the fibrous liquid-crystal polymer present within the matrix. Moreover, because there is substantially no molecular interaction between the fluoropolymer and the liquid-crystal polymer, the interfacial bonding forces between the fluoropolymer and the liquid-crystal polymer are very small. Hence, the greater strength of the liquid-crystal polymer within the fluoropolymer matrix is not transferred to the matrix.
Liquid-crystal polymer reinforced fluoropolymer articles in which the liquid-crystal polymer is well dispersed and reinforces the fluoropolymer are needed.
This need is satisfied by a melt processible fluoropolymer composite article comprising at least one melt processible fluoropolymer, wherein some of said melt processible fluoropolymer contains functional groups, reinforced with fibrous thermoplastic liquid-crystal polymer.